Composite metal article with a platinum coating



March 11, 1969 R. s. RICHARDS 3,432,278

COMPOSITE METAL ARTICLE WITH A PLATINUM COATING Filed July 16, 1985INVENTOR. Pay/14mm fficflq pr BY Q. 7 M ,4

United States Patent 3,432,278 COMPOSITE METAL ARTICLE WITH A PLATINUMCOATING Raymond S. Richards, Toledo, Ohio, assignor to Owens- Illinois,Inc., a corporation of Ohio Filed July 16, 1965, Ser. No. 472,417

US. Cl. 29-1835 Int. Cl. B23p 3/20 2 Claims ABSTRACT OF THE DISCLOSUREThere is disclosed a corrosion resistant metal article comprising a basemetal, a thin intermediate layer of an easily reduced metal, and anouter layer of platinum applied in molten droplet form by means of aplasma-jet spray or flame-spray. The thickness of the platinum layer isat least .007 inch, e.g., .007 to .015 inch. The base metal is iron,nickel, or alloys thereof. The easily reduced metal is copper, silver,or gold.

metal parts which may be subjected to high temperatures and/ orcorrosive atmospheres. Many iron or nickel base alloys exhibitsuflicient thermal resistance so as to be capable of use at fairly hightemperatures; however, in a corrosive atmosphere these metals oxidizeand corrode quickly.

It has been the practice in the past to mechanically clad such basemetals with platinum sheeting. However, one serious drawback is that thethermal expansion characteristics of platinum and the base metals aresuch that there is a tendency for the platinum to buckle and warp undertemperatures in the 2000 F. and above range.

In recent times it has been the practice to flame-spray metals withcoatings of other types of metals. However, in these situations,particularly when an attempt is made to fiame-spray platinum overInconel or other iron or nickel base alloys, the flame used in sprayingthe metal will oxidize the base metal, thus producing a poor bondbetween the platinum and the base metal.

With the foregoing in mind, it is an object of this invention to providea method of metallurgically bonding platinum to base metals.

It is an additional object of this invention to provide a method ofmetallurgically bonding platinum to a base metal by utilizing an easilyreduced metal as an intermediate plated-on layer.

It is a further object of this invention to provide a corrosionresistant metal article having a metallurgically bonded platinumcoating.

Other and additional objects will be apparent from the followingdescription taken in conjunction with the annexed sheet of drawings,wherein:

FIG. 1 is a perspective view of a metal pipe having platinum appliedthereto by my improved method; and,

FIG. 2 is a block diagram illustrating the successive steps of myimproved method.

In accordance with the present invention, applicant has found that basemetals such as iron or nickel base alloys such as Inconel, Nichrome andthe like may be flame-sprayed with platinum successfully to produce ametallurgically bonded, continuous layer of platinum over the base metalwithout the production of pin holes. In accordance with the preferredembodiment of the invention, this is accomplished by first plating thebase metal with a thin, .00025, layer of gold or other noble or easilyreduced metal which will not oxidize or can be reduced duringflame-spraying of platinum thereon. After the gold is plated on the basemetal, a flame-spray or plasma-jet spray technique may be utilized toapply the platinum to the gold to a thickness of .007.015 inch or more.Whether the platinum is applied by the flame-spray or plasma-jet spraytechnique is immaterial so long as there is a deposition of moltenplatinum in droplet form on the gold plated article. After the spraycladding, it is desirable to stress relieve and sinter the compositestructure, for example by heating to 1800" F. for two hours for anInconel-gold-platinum combination. In this particular arrangement thegold serves two purposes 1) it provides a non-oxidized surface for theplatinum and (2) it also serves as a brazing metal in that the platinumdiffuses into the gold and the gold diffuses into the Inconel. Thus ametallurgical bond is established between the Inconel and the platinum.The surface of the base metal may be roughened prior to the gold platingso as to avoid any possibility of the applied platinum separating fromthe base metal during subsequent sintering. Furthermore, it has beenfound desirable and is preferred that the gold plated base metal articlebe preheated to a temperature of approximately 1200 F. and that thespraycladding of platinum be carried out while the plated article ishot. By this technique, the impingement and impact of the platinumdroplets, as they strike the gold plating, will assume a more flattenedcontour since there is a somewhat less temperature difference betweenthe molten platinum particles and the article to be clad. In this mannera more tenacious and better bond will be provided, and the formation ofpin holes or random spots where the platinum, even if sprayed withseveral layers, might provide an intrusion or passage through theplatinum through the gold, is prevented. As can be seen when referringto FIG. 1 of the drawing, the base metal 10, such as Inconel, is platedwith a layer of pure gold 11 and then flame-sprayed or plasma-jetsprayed with platinum to form the coating or cladding 12.

While gold has been disclosed as the preferred metal which is plated tothe clean iron or nickel base alloy, it is also possible to use copperin place of gold. However, when copper is used as the metal plated tothe iron or nickel base alloy, it is necessary to use a reducing gasshield over the plated article prior to the spraying of platinum thereonin order to ensure that the copper does not have an oxide layer orsurface when the platinum is applied thereto. Copper does exhibit theproperty that when it is being flame-sprayed, for example in a platinumflame-spraying system, it tends to lose its oxide coating and appear asa bright metal under the extreme heats involved in the flame-spraying.Thus there is the tendency of the copper to clean itself of oxide duringthe flamespraying of platinum thereon.

A third plating material which may be used in accordance with theinvention is silver. Silver may be plated over the Inconel for example,in a relatively thin layer; however, it would be necessary to heat thesilver-plated article to a temperature sufiicient to decompose all thesilver oxide on the surface of the silver, for example at 1200 -F. Thisheating will effectively clean the silver and permit the flame-sprayingof platinum thereon, with the result that the platinum would adhere andform a metallurgical bond with the silver and the silver in turn wouldmetallurgically bond with the Inconel to produce a metallurgicallybonded article when sintered.

As previously described, the base metal may be roughened prior to theplating of the gold, copper or silver. However, this roughening may notbe necessary, particularly in the situation where the plating is tooccur on the outside surface, for example of a piece of pipe, since thesprayed platinum will shrink tightly around the base metal pipe. Inthose situations where the platinum is to be put on the inside of thearticle such as a pipe, either roughening, preheating or both would berequired in order to keep the sprayed platinum from pulling loose.

In all instances the step of heating to stress relieve and sinter thecomposite article is desirable in order to ensure the production of agood metallurgical bond of the plat inum to the substrate.

Having described the best mode of carrying out the invention, the scopeof the invention should not be limited except as required by the scopeof the appended claims.

I claim:

1. A corrosion resistant metal article comprising a base metal of iron,nickel, or alloys thereof, a thin intermediate layer of a reduced metalselected from copper, silver or gold and an outer layer of platinumapplied in molten droplet form onto the reduced metal so as to bemetallurgically bonded thereto, said outer layer having a thickness ofat least .007 inch.

2. The article of claim 1 wherein the base metal is Inconel, the reducedmetal is gold, and the outer layer has a thickness of .007 to .015 inch.

References Cited UNITED STATES PATENTS 1,704,126 3/1929 Fry 29-1992,459,172 1/1949 Luetkemeyer 29l99 X 2,897,584 8/1959 Schumpelt 29-1993,284,175 11/1966 Spence 29199 X I-IYLAND BIZOT, Primary Examiner.

US. Cl. X.R.

